Radio frequency attenuator



May 26, 1964 E. J. COOK 3,1 4

RADIO FREQUENCY ATTENUATOR Filed March 24, 1961 INVENTOR: EDWARD J. COOKHI ATTORNEY.

United States Patent 3,134,950 RADIC FREQUENCY ATTENUATOR Edward J.Cook, Burnt Hills, N.Y., assignor to General Electric Company, acorporation of New York Filed Mar. 24, 1961, Ser. No. 8,045 3 Claims.(Cl. 333-81) My invention relates to radio frequency attenuators andpertains more particularly to new and improved means for effectivelyattenuating undesired radio frequency currents tending to travel alongthe direct current leads of high frequency electric discharge devices.

Many high frequency electric discharge devices, such as voltage tunablemagnetrons, include several direct current supply leads eitherintegrally formed with or connected to the direct current contacts ofthe devices. Due to various coupling mechanisms that can be present insuch devices, radio frequency currents often tend to travel along or tobe coupled out of the device through the direct current leads. Forconsistent performance and spectral regularity, it is desirable thatthis radio frequency power be attenuated. Additionally, it is desirablethat means be provided which is effective for attenuating undesiredradio frequency power on the direct current leads of an electricdischarge device, and which is adapted for operating at high voltagesand in rarefied atmospheres.

Accordingly, a primary object of my invention is to provide new andimproved means for attenuating radio frequency current on a lead.

Another object of my invention is to provide new and improvedattenuating means whereby attenuation of radio frequency current on alead is greatly enhanced by improving the action of attenuating materialon the electromagentic components of the radio frequency current.

Another object of my invention is to provide new and improved meanseffective for increasing the attenuation per unit length of a leadcarrying radio frequency current to be attenuated.

Another object of my invention is to provide new and improved means forattenuating the radio frequency power on a lead with a minimum totalmass of attenuating material.

Another object of my invention is to provide new and improved means forattenuating the radio frequency power on a lead with improvement in thevoltage breakdown characteristics of the attenuator.

Another object of my invention is to provide a new and improvedattenuator mount structure adapted for mounting a plurality ofattenuators in mutually insulated spaced relation.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide an electricalconductive lead having a section which is bared or devoid of anyelectrically insulative coating. Moulded about the bared section of thelead and in direct intimate contact therewith is a quantity ofattenuating material characterized by high magnetic and high electricallossiness at radio frequencies. The attenuating material is insleeve-like form with a tapered end extending toward the generator ofthe radio frequency waves to be attenuated and, thus, is adapted forconstituting a matched lossy element. In one form of my invention theportion of the lead imbedded in the attenuating material can bestraight. Increased attenuation is obtainable by another form of myinvention wherein the bared section imbedded in the attenuating materialcomprises a coiled section of the lead. Additionally, a modified form ofmy invention constitutes a mount construction for mount- 3,134,950Patented May 26, 1964 ing a plurality of the described attenuators in asingle structure and in a manner wherein the attenuators are mutuallyinsulated and thus adapted for employment in constructions such asvoltage tunable magnetron packages wherein normal operating voltages aresubstantially high. Additionally, my improved mount structure isparticularly effective for resisting arcing over between leads and,thus, is adapted for applications in rarefied atmospheres.

For a better understanding of my invention reference may be had to theaccompanying drawing in which:

FIGURE 1 is an enlarged sectional view of one form of my invention;

FIGURE 2 is an enlarged sectional view of a modified form of myinvention; and

FIGURE 3 is an enlarged sectional view of a lead mount constructedaccording to my invention and adapted for facilitating mounting inmutually insulated relation a plurality of attenuators incorporating theother features of my invention.

Referring to the drawing, I have shown in FIGURE 1 a lead attenuatorgenerally designated 1. The attenuator 1 comprises a length of lead 2which has at least a section designated A which is bared or completelydevoid of insulation. The remaining portion of the lead can be bared asshown or can be insulated.

Provided on the uninsulated or bared section A is a predeterminedquantity of lossy material, or material characterized by high radiofrequency attenuation capabilities. This material can advantageously bemoulded as a generally cylindrical or sleeve member 3 about the lead forimbedding the Section A in the manner shown. Additionally, the lossymaterial is selected to have a maximum magnetic permeability and losstangent. Further, the lossy material is selected to have a maximumdielectric constant and loss tagent, whereby it is adapted for beingelectrically lossy. I have found the attenuating materials availablegenerally under the following designations and from the followingsources to be satisfactorily employable in forming the member 3:

Material Source lolyiron Polyiron In operation, any radio frequencycurrent on the lead is attenuated. This attenuation results to someextent from the electrical lossiness of the material of which sleevemember 3 is formed. However, to a much greater extent the attenuation isattributable to the high magnetic permeability of the sleeve member 3and the effect thereof on the electromagnetic components of the radiofrequency current on the lead.

Coatings of resistive material on a line operate on the electric fieldcomponent in effecting attenuation. However, such coatings do notconcentrate energy as does the attenuating material in my device. In mydevice, and as indicated above, attenuation resulting from operation ofthe electric field components is obtained. However, additionally, andvery importantly, the high magnetic permeability of the sleeve materialin my invention serves to concentrate the magnetic energy in the lossyregion and, thus, has a greater attenuating effect per unit length oflead than would an attenuating structure wherein only resistancematerial is employed.

Additionally, and in recognition of the improvement in attenuationobtainable with a structure wherein the attenuating material operates onthe magnetic components of the radio frequency current, I have providedthe aboveing material.

mentioned direct intimate coextensive contact between the sleevematerial and the bared section A of the lead 2. This constructionaffords a substantially tighter magnetic couple between the sleevematerial and the electromagnetic field components of the radio frequencycurrent, and the tighter magnetic coupling enhances greatly thecapability of the sleeve material in operating on the magnetic fieldcomponents for attenuating the radio frequency current.

Further, I have found that the tighter coupling obtained between thesleeve and lead when the sleeve material is moulded about the bared leadsection enables me to provide an attenuator having a minimum total mass.This advantage is highly desirable where, due to space and wei htconsiderations, the attenuator must be as small and light as possible.Additionally, in some applications, such asthe use of the attenuator onthe direct current lead of a voltage tunable magnetron, it is desirableto keep the 'massto a minimum. Such a device is normally operated withthe use of a static magnetic field extending therethrough and operationcan be adversely affected by the near location of a substantial mass ofmagnetic permeability material.

In the prior art, a sleeve of attenuating material has been slipped overan insulative section of a lead.' In this form or structure theattenuating material is spaced from the wire by the thickness of theinsulating material and aradio frequency leakage path between the wireand attenuating material exists. Additionally, a substantially loosercoupling both electrically and magnetically results, and a substantiallygreater volume of attenuating material is required for attenuating agiven radio frequency current. In my improved structure the attenuatingmaterial is in direct intimate contact with the bared section of thelead, with the desirable result that no radio frequency leakage canoccur between the lead and attenuating material and tighter couplingresults which, in turn, provides for greater attenuation with a reducedmass of attenuating material. 7

As also seen in FIGURE 1, the sleeve 3 is formed with a tapered endsurface 4. The tapered end is provided for being directed toward thesource or generator of the radio frequency wave to be attenuated. Withthe tapered end so oriented sleeve 3 constitutes a matched lossy elementand serves to attenuate undesired radio frequency waves without causingundesired reflection thereof back toward the generator.

The tapered end 4 is particularly effective when its length, designatedB in FIGURE 1, corresponds generally to, or is greater than, the wavelength of the waves to be attenuated. If desired the taper length B canbe made relatively long, whereby broadband matching is obtain able.However, the length B can also be made relatively short whereattenuation of a very narrow band of frequencies is required and whereit is desired to minimize the length and mass of the sleeve 3.

As noted above, the attenuating material is selected for maximumdielectric constant. In such material the Wave length of a radiofrequency wave to be attenuated is substantially shorter than in freespace. Thus, by emp'loying a maximum dielectric constant material, I amable to obtain the desired matching and attenuation with a minimumlength of tapered section. This feature of my invention assists inenabling me to minimize the length and mass of the sleeve 3 required toeffect attenuation of a given radio frequency current.

Illustrated in FIGURE 2 is a modified form of my structure designated 5.This form of my invention is particularly adapted for tightening thecoupling between a bared section C of a lead 6 and a sleeve '7 ofattenuat- In this embodiment the material of the sleeve 7 can be thesame as that described above with respect to FIGURE 1 and the sleeve canalso advantageously be moulded about the lead. Additionally, the sleeve7 includes a tapered section 4' having a length designated D. In thisembodiment the taper can be identical in structure and purpose to thetapered end 4 in FIGURE 1. However, the bared section C of this form ofmy invention constitutes a coiled portion of the lead. This constructionprovides for direct intimate contact or engagement between an increasedlength of the lead and the attenuating material. Thus, it afiordssubstantially increased coupling between the sleeve material and boththe electrical and magnetic components of radio frequency waves on thelead. Accordingly, this form of my invention is adapted for increasedattenuation effects and enables the employment of a reduced mass ofattenuating material in obtaining a given degree of radio frequencyattenuation.

Illustrated in FIGURE 3 is an attenuator mount construction generallydesignated 8 and adapted for mounting a plurality of my improvedattenuators in mutually insulated spaced relation.

The mount construction 8 can be constructed to hold any number ofattenuators. However, in FIGURE 3, I have illustrated an embodimentadapted for holding four attenuators constructed according to myinvention as described above. The attenuators in FIGURE 3 are identicalto that illustrated in FIGURE 1, however, it is to be understood thatthe attenuator 5 illustrated in FIG- URE 2 can be substituted for theones illustrated in FIG- URE 3.

The mount structure comprises an electrically insulative body member 9which can be formed of ceramic or any other suitable high dielectricstrength insulative material. The body member 9 can be suitably mountedin any support such as a wall section It) of a voltage tunable magnetroncavity or operating magnet structure. Additionally, the insulative bodymember 9 includes a plurality of parallel bores generally designated 11.The bores 11 are each formed to include a counterbored section 12wherein an attenuator 3 is positioned so that it is axially whollycontained in bore 11, i.e., the ends of the attenuator are spacedinwardly from the respective ends of the bores 11. In this structure theleads 2 each carry an insulative coating 13 which is stripped back to apoint spaced from the body member 9. A cured quantity of insulativepotting compound 14 is provided on the end surface of. the member 9 andincludes portions 15 which extend into the bores 11 about the baredportions of the leads 2. On the opposite side of the member 9 a secondquantity of cured potting compound designated 16.

is provided which includes portions 17 extending into the counterbores12 about the bared sections of the leads 2. Thus, the attenuators 3 aresealed or encapsulated in the member 9 in a manner which adapts theresultant structure for rarificd atmosphere applications.

In constructing the described potted arrangement, I.

have found particularly eifective the potting compound referred to asGeneral Electric Silicone Rubber-RTV-60 Catalytic 7 potting compound andwhich is available through the General Electric Co., Waterford, NewYork.

The sections or portions of the member 9 between the counterbores 32 aredimensioned and the body material is selected so as to withstandelectrical breakdown between the adjacent attcnuator sleeves 3 at thenormal operof my invention I do not desire my invention to be limited tothe particular forms shown and described, and I intendby the appendedclaims to cover all modifications within the spirit and'scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A radio frequency attenuator for use with direct current leadsadjacent an electrical discharge device, said attenuator consisting of asolid sleeve of a material adapted for attenuating radio frequencyWaves, said attenuating material being characterized by having a highmagnetic permeability and a high dielectric constant, an electricallyconductive lead having a bared section imbedded in said attenuatingmaterial in direct intimate contact therewith, said contact providingtight coupling between said attenuating material and any radio frequencyWave on said lead, said sleeve having at least one externally taperedend, said tapered end being relatively long conpared with the Wavelengthof radio frequency waves to be attenuated.

2. An attenuator mounting and encapsulating assembly for use with directcurrent leads of an electrical discharge device comprising incombination, an insulative member including a plurality of parallelbores extending therethrough, a plurality of attenuators each consistingof a solid sleeve of attenuating material and a conductive lead having abared section extending through said attenuating material in directintimate coextensive contact therewith over the length of said sleeve,said sleeves being of a high magnetic permeability material, at leastone of said sleeves having at least one tapered end adapted to bedirected to the source of radio frequency power to be attenuated 3. In avoltage tunable magnetron having direct current leads connected thereto,a plurality of attenuators for said leads, each attenuator consisting ofa solid elongated quantity of attenuating material having at least onetapered end and characterized by high magnetic permeability and one ofsaid D.C. leads extending through said attenuating material with atleast in intermediate bared section in direct intimate contacttherewith, the portion of said leads on one side of said attenuatingmaterial bearing an insulative coating, an insulative member having aplurality of parallel bores extending therethrough, each of saidattenuators extending through one of said bores with the attenuatingmaterial thereof wholly positioned in said bores and the insulativecoating thereon terminating at a point spaced from said insulativemember, and a quantity of insulative potting material carried on eachside of said insulative member and including portions extending intosaid bores in sealing relation about said bared sections of said leads,and said potting mate'- rial being in sealed overlapping relation withsaid insulative coatings.

References Cited in the file of this patent UNITED STATES PATENTS1,926,807 Hansell Sept. 12, 1933 1,998,525 Russell Apr. 23, 19352,238,915 Peters Apr. 22, 1941 2,412,802 Ford Dec. 17, 1946 2,443,109Linder June 8, 1948 2,538,771 Feenberg Ian. 23, 1951 2,610,250 WheelerSept. 9, 1952 2,782,381 Dyke Feb. 19, 1957 2,898,523 Charles Aug. 4,1959 2,940,058 Foster June 7, 1960 3,002,162 Garstang Sept. 26, 1961FOREIGN PATENTS 587,045 Great Britain Apr. 11, 1947

1. A RADIO FREQUENCY ATTENUATOR FOR USE WITH DIRECT CURRENT LEADSADJACENT AN ELECTRICAL DISCHARGE DEVICE, SAID ATTENUATOR CONSISTING OF ASOLID SLEEVE OF A MATERIAL ADAPTED FOR ATTENUATING RADIO FREQUENCYWAVES, SAID ATTENUATING MATERIAL BEING CHARACTERIZED BY HAVING A HIGHMAGNETIC PERMEABILITY AND A HIGH DIELECTRIC CONSTANT, AN ELECTRICALLYCONDUCTIVE LEAD HAVING A BARED SECTION IMBEDDED IN SAID ATTENUATINGMATERIAL IN DIRECT INTIMATE CONTACT THEREWITH, SAID CONTACT PROVIDINGTIGHT COUPLING BETWEEN SAID ATTENUATING MATERIAL AND ANY RADIO FREQUENCYWAVE ON SAID LEAD, SAID SLEEVE HAVING AT LEAST ONE EXTERNALLY TAPEREDEND, SAID TAPERED END BEING RELATIVELY LONG CONPARED WITH THE WAVELENGTHOF RADIO FREQUENCY WAVES TO BE ATTENUATED.